Kotlin Coroutines Cheat Sheet

import kotlinx.coroutines.*fun main() = runBlocking {    // launch: fire-and-forget coroutine, returns a Job    val job = launch {        delay(1000L)        println("World!")    }    println("Hello,")    job.join() // wait for the coroutine to finish    // async: returns a Deferred<T>, use .await() to get the result    val deferred: Deferred<Int> = async {        delay(500L)        21    }    println("Answer: ${deferred.await() * 2}")}

// suspend functions can call other suspend functions and be paused/resumedsuspend fun fetchUser(id: Int): String {    delay(300) // non-blocking delay, suspends the coroutine    return "User$id"}suspend fun fetchAndPrint(id: Int) {    val user = fetchUser(id) // suspension point    println(user)}// suspend functions can only be called from a coroutine or another suspend funfun main() = runBlocking {    fetchAndPrint(1)}

import kotlinx.coroutines.*class UserRepository {    // CoroutineScope tied to this class's lifecycle    private val scope = CoroutineScope(Dispatchers.IO + SupervisorJob())    fun loadUsers() {        scope.launch {            val users = fetchUsers() // child coroutine            println(users)        }    }    fun cancelAll() {        scope.cancel() // cancels all children started in this scope    }}suspend fun fetchUsers(): List<String> = coroutineScope {    // coroutineScope suspends until all children complete; propagates errors    val a = async { fetchUser(1) }    val b = async { fetchUser(2) }    listOf(a.await(), b.await())}

import kotlinx.coroutines.flow.*fun countdown(from: Int): Flow<Int> = flow {    for (i in from downTo 1) {        delay(100)        emit(i) // suspending emission of the next value    }}suspend fun main() {    countdown(3)        .map { it * 10 }        .filter { it > 10 }        .collect { value -> println(value) } // terminal operator, starts the flow}// StateFlow: hot, state-holder flow with an initial valueval state = MutableStateFlow(0)state.value = 1